The proposed project is part of a long-term goal to understand the mechanisms used by the nervous system for the problems of discriminating and identifying complex sounds. This project proposes to test whether and how temporal coding may be used by cells along the auditory pathway for the encoding and processing of information in complex sounds. In particular, by manipulating temporal patterns across groups of fibers and studying the sensitivity of postsynaptic neurons to those changes, we can determine the degree to which temporal patterns associated with complex sounds influence responses in the auditory system, and the types of information processing performed by the involved mechanisms. Recent physiological experiments have demonstrated that some cells in the cochlear nucleus are sensitive to changes in spatiotemporal discharge patterns across populations of auditory nerve fibers (Carney 1990b). These results will be pursued in this project. First, we win study the sensitivities to spatiotemporal patterns of low-frequency cells in the medial superior olive and the inferior colliculus. Second, we will use high-frequency complex stimuli to study high-frequency members of the anteroventral cochlear nucleus cell groups that have previously been demonstrated to be sensitive to spatiotemporal patterns at low frequencies. Third, a nonlinear model of the auditory nerve that has been developed to study temporal response properties will be extended to investigate the constraints upon the convergent fibers and upon the postsynaptic coincidence mechanism that are necessary to explain the observed sensitivity to different complex sounds. The long-term goal of this research is to aid in developing new strategies for processing sound to aid the hearing impaired. Currently, there are no highly satisfactory hearing aids available that alleviate the difficulties of the hearing impaired for communication, especially in noisy environments. The limitations of today's aids are largely due to our lack of understanding of how the healthy nervous system processes complex sounds such as those used for communication. This project could potentially contribute to our understanding of this process, and thus lead to better strategies for the processing of sounds that could be implemented in new and more powerful hearing aids.